Oil and carbon tend to build up, creating restrictions in the intake manifold. Symptoms will be loss of power (sometimes severe) and poor fuel economy.
Resources for the Repair and Maintenance of your 2012 Volkswagen Jetta TDI
2012 Volkswagen Jetta TDI
2012 Volkswagen Jetta TDI Problems
2012 Volkswagen Jetta TDI Recalls (Recent)
RepairPal Expert Overview:
On the 2.0L TDI common rail Diesel engine/clean Diesel engine, fuel injection pulses could coincide with the natural frequency of injector line #2. This resonance creates additional stress on the fuel line. Small cracks could develop in the #2 injector line, resulting in a Diesel fuel leak. A fuel leak always increases the risk of a fire. Dealers will install an improved #2 fuel injector line and install vibration dampers on all of the injector lines to correct this concern. The Volkswagen/Audi recall number is 23J9/V5.